Dr. Dobb's Journal - May 2008 - (Page 47)

d05zeid_p3db 3/17/08 8:32 AM Page 47 phrases “software,” “source code,” or “correlation.” A query-based elimination filter would be one where the user eliminates all retrieved documents that contain the keyword “correlation.” This would be equivalent to an original query to find all documents with the phrases “software” and “source code” but not “correlation.” There are two reasons in particular that negative query filtering is useful: • If the user were to perform a new query to the search engine, it would require more resources (compute power, storage space, network bandwidth, and so on) than a negative query filter performed on the retrieved objects. For example, the negative query could be done locally on the client computer. • If the query is a best-match query rather than an exact-match query, the negative query filter can be used to get results that may be difficult for users to define with a single query. Threshold filtering involves setting thresholds for displaying the retrieved objects to the user after the information has been retrieved. I define three kinds of threshold filters—relationship thresholds, ranking thresholds, and number thresholds. Combinations of these thresholds are also possible. With a relationship threshold, the value used for determining the threshold is the Ri relationship between the query and the objects. In other words, any object Oi with relationship Ri that is less than threshold T gets eliminated from the results. Ranking threshold filtering can be based on the information display ranking. For example, the Google PageRank criteria can be used such that any object Oi with rank Pi that is less than threshold T gets eliminated from the results. Number threshold filtering is the process of simply reducing the number of objects in the user domain Du to one that is more manageable. It requires that the information retrieval method be a best-match method or that the information display process uses a ranking method. Otherwise, for the exactmatch method, all retrieved objects have equal relationships to the query, and eliminating a specific number of them would have to be arbitrary. Given a number thresh- old N, if the retrieval method is best match, the objects Oi are ordered from highest to lowest by their relationship R i until the number of objects displayed is N. If the retrieval method is exact match but the display process uses a ranking method, the objects Oi are ordered from highest to lowest by their ranking Pi until the number of objects displayed is N. Thresholds need not be minimum thresholds. Maximum thresholds and combinations of minimum and maximum thresholds may be appropriate if the user Figure 1: Information retrieval. JPEG 2000 JPIP, 3D, AND TRANSCODING IMAGE COMPRESSION LIBRARIES · Powerful low-level C libraries · 64-bit & 32-bit, on multiple platforms · Optimized for multiple cores · Lossless and lossy mode · Compressed image optimization for JPIP · Compress to PSNR value or file size · Codestream and file format support · Control progression order, precinct sizes, and tile sizes DOWNLOAD A FULL-FEATURED TRIAL VERSION OF THE PICTOOLS SDK TODAY. Supported across: Microsoft® Windows® LINUX Sun® Solaris IBM® AIX® Contact us for more information. W W W . P E G A S U S I M A G I N G . C O M Pegasus is a registered trademark of Pegasus Imaging Corporation in the United States. The names of actual companies and products mentioned herein may be the trademarks of their respective owners. May 2008 l www.ddj.com l Dr. Dobb’s Journal 47 http://www.pegasusimaging.com http://www.pegasusimaging.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - May 2008

Dr. Dobb's Journal - May 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Software Development Goes to the Movies Cat: A Functional Stack-Based Little Language Mojax: Mobile Ajax Framework Kernel-Mode Databases Getting Better Search Results Effective Concurrency The Agile Edge

Dr. Dobb's Journal - May 2008

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